Radon and indoor air quality at home

Key rules

• Reference level: The reference level for yearly average indoor radon is 300 Bq/m3, and private owners of existing homes have no duty to test.
• Where it matters: Risk is local, and ground-floor homes and basements in listed municipalities are most exposed.
• Best fix: Sub-slab depressurisation is the most effective way to cut radon; retest after any works.
• Combustion heaters: Never run a flueless heater or brasero in a closed room or while you sleep.

Does radon matter where you live?

Radon is a natural gas that seeps out of the ground and can build up indoors. It matters most in ground-floor homes and basements in certain areas. The reference level is 300 Bq/m3 as a yearly average, and private owners of existing homes have no duty to test. Testing is your choice.

Spain's nuclear safety council maps radon risk by municipality. The highest-risk areas are mainly:

• Galicia, especially granite areas.
• Western Castilla y León (Salamanca, Zamora, Ávila).
• Extremadura (north Cáceres, parts of Badajoz).
• The Madrid sierra.
• Parts of Castilla-La Mancha and Andalucía (Sierra Morena, Los Pedroches).
• The Catalan Pyrenees and coastal ranges.
• Some places in the Canary Islands.

Look up your municipality in the council's current list. Being outside a listed zone does not guarantee low radon, because risk depends on the local ground and on the building.

New buildings in listed municipalities must include protection measures. That does not cover an older home you rent or buy.

How to test

Use a passive detector kit. It is a small piece of plastic that you leave in the room you use most. Choose a ground-floor room or a basement room.

• How long: leave it 2 to 3 months, or ideally a year, then post it to the laboratory.
• Where to buy: university laboratories and private accredited firms sell kits. Choose a laboratory with accreditation.
• Cost: a kit usually costs 30 to 80 euros.
• Faster option: electronic monitors give quicker readings but cost more.

Renters should ask the landlord before testing. Ask about the result before you commit to a long lease on a ground-floor or basement home in a listed area.

If your result is above 300 Bq/m3

• Seal and ventilate: close cracks in floors and walls and around pipes and cables. Improve ventilation of the home and of any crawl space. Sealing alone usually gives smaller reductions.
• Sub-slab depressurisation: a sump and fan pull soil gas from under the floor. This is the most effective fix and often cuts radon by 80 to 95 percent. It typically costs 1,000 to 3,000 euros, depending on the building, so get an on-site assessment.
• Retest afterwards to confirm the works worked.

Other indoor air basics

Ventilate every day, even in winter. Open windows for a few minutes to clear moisture and stale air.

Heating matters for air quality too:

• Butane and paraffin (queroseno) heaters have no flue. They release water vapour, roughly one litre of water per kilo of butane burned. They also release carbon monoxide and other gases.
• Do not use them in closed rooms, and never in a bedroom while you sleep.
• Braseros (charcoal or wood braziers) are the most dangerous. They give off carbon monoxide with no flue.
• Electric heaters produce no combustion gases.
• If you use any combustion heater, keep a ventilation opening, choose one with an oxygen-depletion sensor, and fit a carbon monoxide detector.

The warnings and questions below cover common traps and costs.

What to watch out for

• Heaters without a flue can poison you: Butane, paraffin and brasero heaters have no flue and give off carbon monoxide. In a poorly ventilated room, especially a bedroom while you sleep, this can cause poisoning. Braseros are the most dangerous. Do not use them in closed rooms or while asleep. Ventilate when you do use one, fit a carbon monoxide detector, or switch to an electric heater.

• Gas heaters add moisture: Butane gives off roughly one litre of water per kilo burned, which adds damp to the room and can feed mould. Choose electric heating where you can, and air the room regularly.

• Living outside a radon zone does not mean no radon: Radon risk is local and depends on the ground and the building. Ground-floor homes and basements are the most exposed. Look up your municipality in the nuclear safety regulator's list. If you live on a ground floor or in a basement, consider a test kit.

• Nobody will test your home for you: Private owners of existing homes have no duty to test, and the reference level of 300 Bq/m3 is only a target for action. If a test shows a yearly average above 300 Bq/m3, get an on-site assessment of the options to reduce it.

Frequently asked questions

How long does a radon test take?

A radon test usually takes 2 to 3 months, and a full year gives the most reliable result. You place a small plastic detector in the most-used ground-floor or basement room, then send it to a laboratory.

Does a sealed crack fix a radon problem?

Sealing cracks and service entries helps, but it usually reduces radon less than other measures. A system that extracts gas from under the floor slab is the most effective, often cutting radon by about 80 to 95 percent. Retest after any works to see the result.

How much does it cost to reduce radon in an existing home?

A system under the floor slab typically costs about 1,000 to 3,000 euros. The price depends on the building, so ask for an on-site assessment first.

Which areas of Spain have the most radon?

The highest-risk areas are mainly Galicia, western Castilla y León, northern Extremadura, the Madrid sierra, and parts of Andalucía and Catalonia. Look up your municipality in the nuclear safety regulator's list, because being outside a zone does not guarantee low radon.